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IRONMAN 101: Build Your Race-Day Fueling Plan

A primer on how to fuel your body for 140.6 miles, from breakfast through to the run.

byBecky Simon

To say an IRONMAN takes a lot of energy is an understatement. In fact, athletes burn around 7,000 to 10,000 calories during those grueling 140.6 miles. This energy output is staggering when compared to the average human’s calorie needs of 1,500 to 2,500 calories a day. Naturally you’d expect to be in a calorie deficit during race day, as you shouldn’t expect to replace all of those calories out on course. Your mission is to develop a nutrition strategy to maintain adequate fuel stores to compensate for your deficit and stay strong throughout your race.

Going into exercise, your body can store an average of 2,000 carbohydrate calories in the form of muscle and liver glycogen and glucose in your bloodstream. The adage, "breakfast is the most important meal of the day" holds true whether it be race day or before training. Overnight your body burns carbohydrate, so breakfast is the perfect opportunity to top off your carbohydrate stores. If you plan to eat a larger breakfast, eat it two to three hours before the race, which gives your body adequate time to digest. Practice your pre-exercise breakfast routine during training so you know what settles well and how long you need to wait to feel comfortable prior to start racing.

If you prefer a smaller breakfast, fuel up with 200 to 350 calories, 30 to 60 minutes before the race. Eat a carbohydrate-rich breakfast that's easy on your stomach, such as a couple slices of toast with nut butter, an energy bar, a banana and yogurt, or oatmeal with milk and nuts. Right before you take off for the swim, you may want to consume a smaller energy bar (such as IRONMAN's official on-course bar, Bonk Breaker), a gel, or couple of chews for a last minute boost.

Your body has enough carbohydrate stores to fuel about 60 to 90 minutes of endurance exercise. So, as you exit the swim you are most likely already in a calorie deficit. Start fueling during transition or within the first 10 to 15 minutes on the bike. A sports drink, gel, or small snack will help replenish your carbohydrate stores as you ramp up for the next leg of the race.

You may not feel hungry, but you still need to fuel. You can manage your carbohydrate load by fueling consistently and often. The recommended calorie range for exercise lasting over three hours is 45 to 90 grams of carbohydrate (180 to 360 calories) per hour. That means calories—don't get confused by calorie-free electrolyte drinks or caffeine. They do not provide true energy; fuel means calorie! Try to consume a combination of liquid calories and solid calories.

For most athletes, the bike leg is the easiest time to consume solid food. Based on the calorie goals you determine during training, try to settle into your fueling rhythm for the duration of the race. Some athletes like to fuel every 15 to 20 minutes, while others focus on consuming "x" amount of fuel by a specific time period or distance in the race. Dedicate time during training to find the method that works best for you. Many athletes taper solid calories as they near the run leg to avoid GI distress, while other athletes tolerate solid foods throughout the race. Make sure to test your strategy during training.

Training doesn’t stop when your workout is done, so don’t forget to refuel immediately after exercise and maintain a healthy, balanced diet. There is no cookie-cutter solution to your training and race-day nutrition needs, but these guidelines will support you in building your personal nutrition plan.

Becky Simon is a Registered Dietician with Bonk Breaker. This article is sponsored by Bonk Breaker, the Official Bar of IRONMAN. (To find out more about the elite athletes behind the real-food bars, or to purchase bars, go to shop.bonkbreaker.com. Use promo code IM14 to SAVE 10% off all items at the Bonk Breaker store.)